About the Test
Purpose of the test
The serum iron test measures the amount of iron in transit in the body – the iron that is bound to transferrin in the blood. Transferrin is a protein that carries iron in blood. Along with other tests, it is used to help detect and diagnose iron deficiency or overload. Testing may also be used to help differentiate various causes of anemia.
The amount of iron present in the blood will vary throughout the day and from day to day. For this reason, serum iron is almost always measured with other iron tests, including ferritin, transferrin, and calculated total iron-binding capacity (TIBC) and transferrin saturation.
What does the test measure?
Iron is an essential nutrient that, among other functions, is required to produce healthy red blood cells (RBCs). It is a critical part of hemoglobin, the protein in RBCs that binds oxygen in the lungs and releases it as blood circulates to other parts of the body. The serum iron test measures the amount of iron in the liquid portion of blood.
Serum iron is almost always measured with other iron tests, such as serum ferritin, transferrin, TIBC, unsaturated iron-binding capacity (UIBC), and transferrin saturation (%). These tests are often ordered simultaneously, and the results are interpreted together to help diagnose and/or monitor iron deficiency or overload.
The body cannot produce iron and must absorb it from the foods we eat or from supplements. Once absorbed, it is transported throughout the body by binding to transferrin, a protein produced by the liver.
If you are healthy, most of the iron absorbed is incorporated into the hemoglobin inside developing RBCs in the bone marrow. The remainder is stored in the tissues as ferritin or hemosiderin, with additional small amounts used to produce other iron-containing proteins such as myoglobin and some enzymes.
When the level of iron is insufficient to meet the body’s needs, the nutrient level in the blood drops, and iron stores are depleted. This may occur because:
- Not enough iron is consumed (either foods or supplements)
- The body is unable to absorb iron from the foods eaten in conditions such as celiac disease
- There is an increased need for iron, such as during pregnancy or childhood
- There is a condition that causes chronic blood loss (e.g., peptic ulcer, colon cancer, excess menstrual bleeding)
Insufficient levels of circulating and stored iron may eventually lead to iron deficiency anemia (decreased hemoglobin). In the early stage of iron deficiency, no physical effects are usually seen, and the amount of the nutrient stored may be significantly depleted before any signs or symptoms of deficiency develop.
If you are otherwise healthy and anemia develops over a long period, symptoms seldom appear before the hemoglobin in the blood drops significantly below the lower limit of normal.
However, as the iron-deficiency progresses, symptoms eventually begin to develop. The most common symptoms of anemia include fatigue, weakness, dizziness, headaches, and pale skin.
On the other hand, too much iron can be toxic to the body. Iron blood levels and storage increase when more of the nutrient is absorbed than the body needs. Absorbing too much iron can lead to progressive accumulation and damage to organs such as the liver, heart, and pancreas.
An example of this is hemochromatosis, a genetic disease in which the body absorbs too much iron, even on a normal diet. Additionally, iron overdose can occur when someone consumes more than the recommended amount.
When should I get this test?
Serum iron tests may be ordered as follow-up tests when results from a complete blood count (CBC) show that your hemoglobin and hematocrit are low. Also, your red blood cells are smaller and paler than normal (microcytic and hypochromic), suggesting iron deficiency anemia even though other clinical symptoms may not have developed yet.
Testing may be ordered when you develop signs and symptoms of anemia, such as:
- Chronic fatigue/tiredness
Testing may be ordered when iron overload is suspected. Signs and symptoms will vary from person to person and tend to worsen over time. They are associated with iron accumulation in the blood and tissues. These may include:
- Joint pain
- Fatigue, weakness
- Lack of energy
- Abdominal pain
- Loss of sex drive
- Organ damage, such as in the heart and liver
When a child is suspected to have ingested iron tablets, a serum iron test is ordered to detect and help assess the severity of the poisoning.
Iron tests may also be ordered periodically when iron deficiency or overload is being treated to evaluate the effectiveness of treatment.
Finding an Iron Test
How can I get an iron test?
Iron testing is usually performed at a doctor’s office or another medical setting like a hospital or laboratory. The tests are typically ordered by a doctor but may be available without orders from your doctor at a walk-in lab.
Can I take the test at home?
As a diagnostic test requires a blood draw, taking an iron test at home is very difficult. You can check for a mobile phlebotomist service in your area which can take the sample from the comfort of your home and deliver it to a local laboratory for testing. But this service isn’t always available.
How much does the test cost?
The cost of an iron test will vary depending on factors such as where the test is done and whether you have health insurance. When ordered by a doctor, insurance typically covers the test, although you may have to pay a copay or deductible. Your doctor’s office, lab, and health plan can provide information about any out-of-pocket costs that may be your responsibility.
Taking the Iron Test
The iron test usually requires a blood sample, which is usually taken from your arm in a doctor’s office, health clinic, hospital, or lab. But a saliva sample can also be accepted depending on the type of test available.
Before the test
You may be instructed to have your blood drawn in the morning and/or fast for eight to 12 hours before sample collection; in this case, only water is permitted. Follow any instructions from your health care practitioner and/or from the laboratory performing the test.
During the test
A blood sample is taken from a vein in your arm. The person taking the sample may tie a band around your upper arm and will clean the area where the needle will be inserted into your skin. A small amount of blood is drawn into a tube. You may feel a slight sting when the needle enters your skin.
The process of taking a blood sample usually takes less than three minutes.
After the test
At a doctor’s office or laboratory, you will be asked to apply gentle pressure to the site with a bandage or a piece of gauze after the needle is withdrawn. This will help stop bleeding and may prevent bruising. Next, the site will be bandaged. You may resume your normal activities following the test.
A blood draw is a very low-risk procedure. You may have slight bruising at the site where the blood sample was taken.
Iron Test Results
Receiving test results
The doctor who ordered your iron test may share the results with you, or you may be able to access them through an online patient portal. Iron results are usually available within a few business days.
Interpreting test results
Serum iron levels are often evaluated in conjunction with other iron tests. A summary of the changes in iron tests seen in various diseases of iron status is shown in the table below.
The early stage of iron deficiency is the slow depletion of stores. This means there is still enough iron to make red cells but the stores are being used up without adequate replacement. The serum iron level may be normal in this stage, but the ferritin level will be low. Ferritin level reflects the total amount of stored iron in the body.
As iron deficiency continues, all of the stored iron is used and the body tries to compensate by producing more transferrin to increase iron transport. The serum iron level continues to decrease and transferrin and TIBC and UIBC increase. As this stage progresses, fewer and smaller red blood cells are produced, eventually resulting in iron deficiency anemia.
If the iron level is high, the TIBC, UIBC, and ferritin are normal and you have a clinical history consistent with iron overdose, then it is likely that you have iron poisoning. This occurs when a large dose of iron is taken all at once or over a short period of time. Iron poisoning in children is almost always acute, occurring in children who ingest their parents’ iron supplements. In some cases, acute iron poisoning can be fatal.
If you have mutations in the HFE gene or another iron regulation gene is diagnosed with hereditary hemochromatosis. Yet while many people who have hemochromatosis will have no symptoms for their entire life, others will start to develop symptoms such as joint pain, abdominal pain, and weakness in their 30s or 40s. Men are affected more often than women because women lose blood during their reproductive years through menstruation.
Iron overload may also occur if you have hemosiderosis and have had repeated transfusions. This may occur with sickle cell anemia, thalassemia major, or other forms of transfusion-dependent anemia. The iron from each transfused unit of blood stays in the body, eventually causing a large buildup in the tissues. If you have alcoholism and chronic liver disease you may also develop iron overload.
You may want to ask your doctor the following questions:
- Do all people with iron deficiency have anemia?
- What foods/supplements can I eat to increase the iron in my diet?
- Does donating blood affect my iron levels?
- How long does it take for treatment to be effective? Will I be able to tell it’s working?